The present invention relates generally to record disc recording systems and more particularly to systems which import a predistortion during recording, to prevent tracing distortion during reproducing.
In general, the sound groove of a record disc is formed by cutting a V-shaped groove. The reproducing system traces the sound groove with a pickup reproducing stylus having a circular cross section at the part which contracts the walls of the sound groove. For this reason, the path of the tracing tip, of the reproducing stylus, differs from the track of the tip of the recording stylus. A so-called tracing distortion is generated in the reproduced signal, whereby the tone quality of the reproduced sound deteriorates greatly.
In a four-channel record disc in an angle-modulated wave of a wave band outside audio-frequency, is recorded by being multiplexed with a direct-wave signal. The tracing distortion causes, not only a deterioration of the tone quality in the reproduced sound, but also an interference of the angle-modulated wave by a distortion component of the direct-wave signal. These distortions give rise to an admixing of an extraneous signal component in the demodulation output of the angle-modulated wave or a generation of abnormal sound, due to interference.
Accordingly, an object is to eliminate the effect of tracing distortion, at the time of reproduction. To do this, the recording signal is given a pre-distortion which is complementary to the tracing distortion which is generated at the time of reproduction.
One method used heretofore has used for this measure has introduced a distortion which is a direct simulation of the state of the reproducing stylus tip. Examples of systems using this method are the so-called correlator and the skew sampling systems, for distortion signal recording.
In the correlator system, however, elaborate delay circuits and gate circuits are required. The electrical circuitry has been disadvantageously complicated. Particularly, as in a four-channel record disc system, an amply flat amplitude characteristic and a linear phase characteristic are required until a high frequency range (for example, 45 KHz) is reached. The transmission characteristics of the delay circuits themselves must be amply good. Moreover, a large number of unit delay circuits are necessary.
In the skew sampling system, sampling is necessary. In order to apply this system to the four-channel record disc system, it is necessary to use a suitably high sampling frequency. This is difficult to carry out in practice. Even if it is possible, other problems are encountered, such as a highly expensive circuitry.